5 Insane Ways Animals Changed the Course of Humanity

#2. Cows Trained Us to Digest Dairy

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Something that Europeans and their descendants do that you might not realize seems downright bizarre to the rest of the world is that we like to drink cool glasses of that white stuff that comes out from under a cow. That's because most of the non-white population of the world -- 50 percent of Mediterraneans, 95 percent of Asians, and close to 100 percent of Native Americans -- are lactose intolerant. On the other hand, 90 percent of Europeans can drink milk just fine. So why whitey? Simply, early Europeans spent more time around cows.

David De Lossy/Photodisc/Getty Images"I consider myself more a citizen of the world, thank you."

Humans, like every other mammal, were never designed to drink milk past infancy. Normal people (and considering the global statistics, it's the lactose intolerant who are the normal people) lose the ability to digest milk at around 5 years old. That's when we stop producing the enzyme lactase, which breaks down the milk sugars known as lactose. Without that, the lactose in milk just goes straight to our colon and reinvents itself as the Hershey squirts.

James Woodson/Photodisc/Getty Images"In retrospect, this was way too much to do for a Klondike bar."

But after white Europeans and cultures around the Middle East domesticated cattle around 7,500 years ago, they started dabbling in drinking their milk. Those few who were able to tolerate it had an evolutionary advantage, having access to an abundant new source of protein and vitamin D. Since those who drank their milk grew big and strong, the ability to digest it spread around cattle farming communities until most people who spent a lot of time around cows grew to enjoy it without running to whatever passed for a bathroom back then.

For the rest of the world who preferred to obtain their nutrition in ways that didn't involve sucking on a cow's tits, their lactose intolerance remained just as it was. So if you've enjoyed some cheese recently, you know who to thank.

#1. Fleas Might Save Us from HIV

Because of their willingness to bite human and animal alike, fleas are extremely good at spreading disease. Countless human deaths can be attributed to their two most lethal gifts, the Black Death and smallpox. But here's the kicker -- by infecting us with these horrors back in a more classical period of history, fleas helped a bunch of us develop an immunity to HIV, and in doing so might help us find a cure for good.

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"All in a day's work."

HIV is a virus that destroys the immune system by infiltrating immune cells, which it can only do by going through a very specific opening in the cell wall, kind of like how Luke blew up the Death Star. Once all your body's Death Stars have been destroyed, you have the disease known as AIDS, which means that you have no immune system, and that's really bad. Really bad.

What's this got to do with fleas? Well, it turns out that the Black Death and smallpox infiltrate your cells in the exact same way. Back when these diseases ravaged the globe and killed almost everyone, there were a few people who, through random chance, had a genetic immunity (i.e., their little Vaders remembered to shut off the damn exhaust ports). Eliminating vast numbers of people who weren't immune allowed the resistance to spread through natural selection -- which, incidentally, also made them resistant to HIV. That's why today 10 to 18 percent of humans of European descent are either immune or resistant to HIV.

The discovery of this mutation has led researchers to the creation of an antiviral medication called maraviroc and is helping them create the first ever HIV cure. So thanks, fleas; your murderous, infection-spreading lifestyle might just cure one of the worst human diseases ever.

Zac Eckstein is a writer, web designer, and circus employee in Seattle. You can find him on Facebook or, if you like art, you can visit his website at theseattlevine.com.